1. Field of the Invention
The present invention relates generally to data transmission apparatus, and more particularly, to a data junction and branching mechanism for an asynchronous data transmission path.
2. Description of the Background Art
Data processing apparatuses such as data flow type information processors employ asynchronous data transmission paths. In such data processing apparatus, a junction mechanism for merging a plurality of data packets is used for transmitting data packets applied from data transmission paths in a plurality of preceding stages to a data transmission path in one succeeding stage. For transmitting data packets applied from a data transmission path in a preceding stage to data transmission paths in a plurality of succeeding stages, a branching mechanism for sequentially branching the respective data packets. A junction and branching mechanism including a junction mechanism and a branching mechanism is used for transmitting each of a plurality of data packets applied from data transmission paths in a plurality of preceding stages to any of data transmission paths in a plurality of succeeding stages.
FIG. 17 is a block diagram showing a conventional data transmission apparatus for merging a plurality of data packets applied from transmission paths in two preceding stages to a transmission path in one succeeding stage. Such data transmission apparatus is disclosed in Japanese Patent Laying-Open No. 62-265738 and the corresponding U.S. patent application Ser. No. 260,068 now U.S. Pat. No. 4,985,890.
An n-bit packet data applied from an A port is transferred to a data transmission path 170 through data transmission paths 110, 120 and 130. An n-bit packet data applied to a B port is transferred to the data transmission path 170 through data transmission paths 140, 150 and 160. When the packet data from the A port contends with packet data from the B port, the packet data arriving first,is first transferred to the data transmission path 170 by the control of an arbitration control portion 220.
Operation will be described in a case where packet data from the A port arrives prior to packet data from the B port.
Packet data is applied to the data transmission path 110 in response to a transmission signal C110. As a result, a transmission acknowledging signal AK110 enters an inhibited state. When a transmission acknowledging signal AK120 is at an acknowledged state, the packet data is transferred to the data transmission path 120 in response to a transmission signal C120. As a result, the transmission acknowledging signal AK120 enters an inhibited state. When a transmission acknowledging signal AK130 is at an acknowledged state, the packet data is transferred to the data transmission path 130 in response to a transmission signal C130. As a result, the transmission acknowledging signal AK130 enters an inhibited state.
The arbitration control portion 220 renders a transmission acknowledging signal AK171 acknowledged and a transmission acknowledging signal AK172 inhibited in response to the transmission signal C130 and the transmission acknowledging signal AK130 when a transmission acknowledging signal AK170 is at an acknowledged state.
Meanwhile, packet data is applied to the data transmission path 140 in response to a transmission signal C140. As a result, a transmission acknowledging signal AK140 enters an inhibited state. When a transmission acknowledging signal AK150 is at an acknowledged state, the packet data is transferred to the data transmission path 150 in response to a transmission signal C150. As a result, the transmission acknowledging signal AK150 enters an inhibited state. When a transmission acknowledging signal AK160 is at an acknowledged state, the packet data is transferred to the data transmission path 160 in response to a transmission signal C160. As a result, the transmission acknowledging signal AK160 is inhibited.
With the transmission acknowledging signal AK171 acknowledged and the transmission acknowledging signal AK172 inhibited, data transfer from the data transmission path 130 to the data transmission path 170 is acknowledged to cause data transfer from the data transmission path 160 to the data transmission 170 to stand by. After the packet data is transferred from the data transmission path 130 to the data transmission path 170 in response to a transmission signal C171, the transmission acknowledging signal AK172 is acknowledged to transfer the packet data from the data transmission path 160 to the data transmission path 170.
FIG. 18 is a block diagram showing a conventional data transmission apparatus which branches packet data applied from a transmission path in one preceding stage out into transmission paths in two succeeding stages in turn. This data transmission apparatus is disclosed in Japanese Patent Laying-Open No. 62-265740 and the corresponding U.S. patent application Ser. No. 259,850 now U.S. Pat. No. 5,133,051.
Packet data applied to a data transmission path 180 is transferred to either a data transmission path 200 or 210 through a data transmission path 190 and output to a C port or a D port.
Packet data is applied to the data transmission path 180 in response to a transmission signal C180. As a result, a transmission acknowledging signal AK180 is inhibited. When a transmission acknowledging signal AK190 is acknowledged, the packet data is transferred to the data transmission path 190 in response to a transmission signal C190. As a result, the transmission acknowledging signal AK190 is inhibited.
Meanwhile, a branch destination specifying bit BR is previously applied to a comparison and determination logic portion 230. Each packet data includes an identifier. The comparison and determination logic portion 230 compares an identifier included in packet data with the branch destination specifying bit BR and applies the comparison result to a branch control portion 240. The branch control portion 240 activates either of activation signals EA or EB based on the comparison result.
It is assumed, for example, that the activation signal EA is activated. In this case, when a transmission acknowledging signal AK200 is acknowledged, packet data is transferred from the data transmission path 190 to the data transmission path 200 in response to a transmission signal C200. Conversely, it is assumed that the activation signal EB is activated. In this case, when a transmission acknowledging signal AK210 is activated, packet data is transferred from the data transmission path 190 to the data transmission path 210 in response to the transmission signal C200.
As described above, the junction and branching mechanism is structured by combining the data transmission apparatuses shown in FIGS. 17 and 18.
The entire performance of the junction and branching mechanism using the data transmission apparatuses shown in FIGS. 17 and 18 is determined by the maximum flow rate of packet data merged in the data transmission path 170. More specifically, packet data input is allowed up to the maximum flow rate of the data transmission paths 170, 180 and 190 through which the merged packet data flow. Therefore, when packet data are to be simultaneously input to a plurality of data transmission paths on the input side, packet data are not allowed to be input at the maximum flow rate of each data transmission path. As a result, a flow rate of input packet data is inevitably reduced. In a case of junction of packet data from n ports, for example, a flow rate of allowable packet data to be input to each port is reduced to 1/n. In this case, a buffer should be provided.